The lead was short lived as Mount laid on Martyn Waghorn's leveller after 27 minutes before Fabregas' victor.
The visitors made several changes after losing to Manchester City in the Premier League at Wembley 48 hours earlier but managed to carve out a two-goal lead through South Korean Son.
Despite the defeat that knocked them out of the competition, Lampard and his Derby County side can keep their head up high and brimming with pride as they put in a performance that was the ideal testament to their ambition under the new manager.
"He is looking quite good for the weekend [the home game with Crystal Palace on Sunday]".
Gianfranco Zola afterwards played down the notion that Chelsea's edge had been blunted by playing in a stadium chanting for the opposition manager, instead crediting Lampard's game plan of blocking passes into Cesc Fabregas and forcing those behind him into uncomfortable decisions.
Not the children ducking and weaving between doorways down the Fulham Road in search of Halloween candy, but Mason Mount and Fikayo Tomori, Chelsea's two loanees featuring in something of an audition against their parent club.
Chelsea have put a lot of emphasis on being successful in all competitions this season, including the Carabao Cup.
Yet while Derby were obliging, they always carried a potent threat of their own with Mount and Harry Wilson pesky.
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The Prime Minister said Sardar Patel, a veteran administrator, had also popularised the idea of cooperative housing societies. The current tallest statue in the world-the 502ft high Spring Buddha Temple in China-will be eclipsed by the 597 ft.
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Needless to say, things aren't great right now for the Wine and Gold, and now Kevin Love is dealing with reported foot soreness. Oklahoma led 50-34 at halftime after Boston had shot just 32 per cent and missed all 11 three-point attempts.
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Each package had six Forever stamps on the envelope as well. "Let's say for example, that maybe these bombs aren't operational". According to sources, the explosive device was a PVC pipe with a timer (probably a digital alarm clock) to run the detonator.
The Italian admitted that Barkley was developing Lampard's goalscoring touch, but played down the comparisons, for the time being, saying: "I thought Frank Lampard getting in the box was exceptional". But, thankfully, the draw for the quarter-finals will occur directly following Chelsea's game against Derby County on Sky Sports, live from Stamford Bridge.
Predicted Derby County XI: Carson; Bogle, Tomori, Keogh, Forsyth; Wilson, Huddlestone; Waghorn, Mount, Lawrence; Nugent.
5' - OWN-GOAL! Chelsea 1-0 Derby: Well, would you believe it? That's why he scored so many goals. "So we didn't have control of the game".
Ruben Loftus-Cheek could start as a result and Mateo Kovacic could play to try to play himself into form.
Having memorably beaten Manchester United at Old Trafford, the Chelsea fans perhaps had the comfort of knowing their admittedly weakened side should still have too much for the Championship club.
The only thing missing from Mount's performance was a goal - seeing a Lampard-esque effort from 25 yards deflect narrowly wide and another saved low down by Willy Caballero.